Sounds like it will need rockers adjusted. Not sure if they are hydraulic or solid lifters.
Congrats on getting it running!
If it is indeed a 57 car engine, then it would have hydraulic lifters
Hard to tell from the video exactly, but that 'knocking' sure sounds a lot worse than simply tappets - sounds like a rod end or main bearing. I would have thought your local expert would have recognized serious noise however, so maybe I'm (hopefully) wrong.
I'm sure our resident experts will weigh in
